Conventionally, there has been known a semiconductor device having a so-called shield gate structure (see patent literature 1, for example). As shown in FIG. 21A, a conventional semiconductor device 900 includes: a semiconductor base body 910 having an n+ type drain region 912, an n− type drift region 914, a p type base region 916 and an n+ type source region 918; a trench 922 formed in the inside of the semiconductor base body 910, having a bottom disposed adjacently to the n− type drift region 914 and a side wall disposed adjacently to the p type base region 916 and the n− type drift region 914, and formed into a stripe pattern as viewed in a plan view; a gate electrode 926 disposed in the inside of the trench 922 and opposedly facing the p type base region 916 with a gate insulating film 924 interposed therebetween on a portion of the side wall; a shield electrode 930 disposed in the inside of the trench 922 and positioned between the gate electrode 926 and the bottom of the trench 922; an electric insulating region 928 disposed in the inside of the trench 922, the electric insulating region 928 expanding between the gate electrode 926 and the shield electrode 930, and further expanding along the side wall and the bottom of the trench 922 so as to separate the shield electrode 930 from the side wall and the bottom; a source electrode 934 formed above the semiconductor base body 910 and electrically connected to the source region 918 and the shield electrode 930; and a drain electrode 936 formed adjacently to the n+ type drain region 912.
The conventional semiconductor device 900 includes the shield electrode 930 disposed in the inside of the trench 922 and positioned between the gate electrode 926 and the bottom of the trench 922. Accordingly, a gate-drain capacitance CGD (see FIG. 21B) is lowered. As a result, a gate charge current amount and a gate discharge current amount are lowered and hence, a switching speed can be increased. Further, a distance between a corner portion of the trench 922 where the concentration in an electric field is liable to occur to the gate electrode 926 can be increased. Still further, an electric field can be attenuated in the electric insulating region 928 and hence, a withstand voltage can be increased.